I don't think one can produce an answer to "who is right" as topics like this, steeped in mysticism and tradition are not so clearly delineated as right and wrong in an objective, transcendent way.
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DannoJul 2 '12 at 16:44

i'm surprised that no one has made a reference to the red string tied around the wrist of Zerach as he was born - bereshis 39:28 and subsequently used by Rachav as a protective sign
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user1668Aug 30 '12 at 20:36

"Per Tosefta it is a prohibited practice" What is "it"? The Tosefta mentions a red string on the finger. But the red string commonly practiced today is around the wrist.
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CuriouserJul 2 '12 at 17:02

Perhaps that is why there are those that allow it.
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Gershon GoldJul 2 '12 at 17:08

@Curiouser, A lot of people (most, perhaps) wear the red string on the wrist, as you stated. But many others tie the red string to their backpacks, other jewelry, their hair, etc. I believe most people associate the issue, whether they support it or oppose it, with the string itself, not any particular way of wearing it. Perhaps the wrist was just seen as less obtrusive and developed as a common way of wearing it from the root (or formerly more common way) of wearing it on a finger.
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Seth JJul 2 '12 at 17:34

@HachamGabriel I don't think that's ever how it's used in the gemara. Perhaps others have since used it to imply that position, but IMO doing so is disingenuous at is gives the impression that the gemara contains such an explicit klal. (I'm not debating whether the klal is a good one; only the use of the phrase to imply it.)
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Double AA♦Jul 4 '12 at 4:05

A "Kalava" is the sacred Hindu thread also called 'mauli' in hindi. It is worn while performing Hindu rituals like Yajna or Puja. It is tied by a priest on the wrists of all the people attending the prayer ceremony. Kalava is tied on right hand of males and unmarried females, and on left hand of married females. Sometimes it has small yellow parts in between the mostly red string. It sometimes has knots which are tied up while reciting Sanskrit mantras to invoke God and is worn to ward off evil from the person who wears this red thread.

It spread to Judaism and was adopted by superstitious people, just as it was back in the times of the Tosefta (see other answer).